Heat exchangers are used in a wide variety of products and processes to efficiently transfer heat from a higher temperature fluid to a lower temperature fluid, often without mixing the fluids. Heat exchangers are often simple mechanical devices with no moving parts. Heat exchangers are employed in a wide variety of industrial processes, including refining and manufacturing processes, and are present in many products, including vehicles, computers, power electronics, medical equipment, and weapons systems.
Heat exchangers can be categorized based on flow arrangement and construction type. Common flow arrangements include parallel-flow, counter-flow, and cross-flow. In a parallel-flow arrangement, hot and cold fluids enter at the same end of the heat exchanger and flow in the same direction. In a counter-flow arrangement, hot and cold fluids enter at opposite ends of the heat exchanger and flow in opposite directions. In a cross-flow arrangement, hot and cold fluids flow perpendicular to each other through the heat exchanger. Common construction types include concentric tube, shell-and-tube, fin-tube, rotating wheel, and plate-fin.
Heat exchanger can be designed to transfer heat from liquids to liquids, gases to gases, or liquids to gases. In liquid-to-gas heat exchangers for computer cooling, the liquid is often water and the gas is often air. These liquid-to-gas heat exchangers suffer poor gas-side performance due to low thermal conductivity and low thermal capacity of the air flowing through the heat exchangers.